Incident Overview
While in cruise flight shortly after entering foreign airspace, the flight crew received an alert indicating a System B hydraulic failure. In response, they decided to return to and land in the United States. Upon re-entering US airspace, the crew declared an emergency and requested to land at the departure airport.
Approach and Secondary Failure
During the final approach, approximately five minutes after selecting flaps to 15 and lowering the landing gear, the crew received an alert showing the System A hydraulic quantity gauge had dropped to zero pounds per square inch. Subsequently, both System A LOW PRESSURE lights illuminated, and the airplane entered manual reversion mode. The flight crew reported that the airplane became difficult to control, yet they managed to land uneventfully at the airport.
Investigation Findings
Maintenance personnel from the airline and the aircraft manufacturer inspected the hydraulic systems. They determined that the initiating event was a failure of an engine-driven pump. The secondary event was a crack in a hydraulic line that failed due to fatigue. A metallurgical examination revealed that the fatigue fracture originated at the toe of the welding root, where a crack had propagated through half the circumference of the tube.
Corrective Action
As a result, the airframe manufacturer redesigned the affected tube. The original titanium tube, part number 272A4451-87, was replaced with a stainless steel tube, part number 272A4451-200.